Excellent progress was made in continuing the development of new hybrid rootstocks for the Florida citrus industry. Highest priority is being placed on work to develop hybrid rootstocks that can be made available for release to growers in the next three years, including selections from about 300 Supersour-type rootstock selections. It is expected that two of these Supersour rootstocks will be released in 2018, and at least two more in 2019-20, as further information is collected from ongoing field trials, and clean source material is available from from FDACS-DPI. During this quarter, one new replicated rootstock field trial was planted on East coast flatwoods site. The trial used Valencia scion and included statistically randomized replicates of 72 different rootstocks, with most rootstocks represented by 12 replications. Standard rootstocks included for comparison were Sour orange, Swingle, Cleopatra, and Ridge. Emphasis in the new trial was on SuperSour selections for which preliminary performance information is promising and that are in the DPI clean source program. Trees in the nursery were in the final stages of preparation for planting two additional field trials in the coming quarter. The trials will each include 8-12 replicates of about 60 new rootstocks, along with several standard rootstocks for comparison. Emphasis in these new trials is also on SuperSour selections for which other performance information is promising and that are in the DPI clean source program. Liners were prepared in the nursery by seedage and cuttings for additional field trials to be prepared for future plantings, based on new hybrid rootstock selections that look the best with HLB in preliminary field sites. About 600 additional seed source trees were planted into the field for these new promising selections, so that more seed will be available from the SuperSour rootstocks for commercial use after release. Research was conducted in collaboration with commercial nurseries and tissue culture propagation facilities to study and compare rootstock liners produced from seed, cuttings, and micropropagation. The rapid expansion in the demand for the newest rootstocks following release makes it clear that available seed for these new rootstocks will frequently be inadequate to satisfy commercial demands. Preliminary propagation information suggests that more US-942 rootstock will be propagated by micropagation than seed in the 2017-18 season. It is likely that cuttings and micropropagation of rootstocks will become increasing common. Noted differences in nursery performance of liners by propagation type, have prompted concerns about the influence of propagation type on field performance. We have initiated research to study these issues and address the concerns in a way that provides clear answers to growers and nurseries. One field trial containing rootstocks propagated by the three methods will be planted in the coming quarter. Performance data was collected from several field trials, including tree size, canopy health, and infection status by qPCR. Extensive cropping and fruit quality data will be collected from trials beginning the the next quarter. Analysis of results from previously established trials indicates that HLB introduces more complex variability to trials than that observed without HLB. This means that more than five or six statistical replicates will be needed to provide clear evidence of superior rootstock performance. Based on this observation, new USDA rootstock trials will usually include more than six statistical replications, regardless of the number of trees per replication. Using valid statistical comparisons is essential to develop reliable information about relative rootstock performance in field trials and should be the foundation of grower rootstock selection for new field plantings. I am working with the UF breeding team under two HLB-MAC projects to establish at least 13 additional rootstock field trials over the next 12 months, combining the best advanced new rootstocks from the USDA and UF breeding programs. The first of these trials will be field planted at the USDA Ft. Pierce Farm in the next quarter. Additional information is available on the USDA rootstock breeding project, on request.